The reciprocating compressors present a connecting rod, having a smaller eye, which is articulated, through an articulating pin, to a piston that reciprocates inside the cylinder of the compressor, and a larger eye, mounted to an eccentric end of a crankshaft, which is orthogonal to the piston stroke, the other end of said crankshaft supporting the rotor of an electric motor, whereas the stator of the motor is supported on a cylinder block, lodging the bearing of the crankshaft, the block being mounted inside a case, by means of springs, said case being closed by a cover, which defines a sealed unit.
In order to obtain a better performance of the compressor, it is important, from the mechanical point of view, that the parts with relative movement present perfect adjustments of their geometries, so as to avoid leakage, wear and tribological effects that lead to a loss of volumetric yielding.
The perfection in the geometry of the parts is verified, for example, in the maintenance of the piston cylindricity.
Alterations in this characteristic of the piston affect the operation of the compressor.
The attachment between the pin and the piston in the known techniques (mechanical mounting by interference, resilient pin, gluing, etc.) affects the yielding of the reciprocating compressors, mainly due to the deformations caused by the loss of symmetry and to problems that occur in the piston--pin--connecting rod assembly and cylinder, said problems resulting in vibrations, noises and loss of volumetric yielding (leakages).
The smaller the parts used in the mounting operation, with more precision being required for such parts, the more enhanced will be the above cited deficiencies. Among said known techniques, those which use additional fastening components, such as pins and rings or bonding material, as in the gluing technique, cause localized tensions and, above all, unbalance in the piston--pin--connecting rod assembly, which also impairs the performance of the compressor.
The conventional welding technique, besides presenting the inconvenience of incorporating additional material and causing residues, thereby deforming the piston during the melting operation, should not be applied to materials with different physical characteristics (melting point), such as the tempered or sintered materials. Moreover, this process of fixation is difficult to apply in small systems, as in the case of the hermetic compressors, more specifically in the piston--pin--connecting rod assembly thereof.
The fixation through adhesives, though not presenting the inconvenience of residues, as in the fixation by welding, requires a thorough cleaning of the surfaces to be welded and a determined time for the adhesive cure, which time, in spite of being reduced by the application of catalysts, does not avoid the problems caused to the sequential mounting process of the compressors. Moreover, physical-chemical deteriorations lead to the accelerated aging of the adhesives, as a function of the conditions of the compressor operation, thus substantially reducing its strength and affecting the reliability in the mounting operation of said compressor.